There are two main types of piston driven reciprocal internal combustion engines, they are the spark ignition engines, and the auto-ignition engines, also called diesel engines.
These piston driven reciprocal engines, for the most part, use either a two-stroke cycle or more commonly, a four-stroke cycle. The main parts of these engines are; a cylinder containing a piston with a reciprocal movement which is converted into a rotational movement by means of a connecting rod and a crankshaft, and a cylinder head consisting of at least two valves, one exhaust valve and one intake valve. The four stroke or four cycle engine begins by the piston drawing an atomized air-fuel mixture into the cylinder through the intake valve on the first down stroke, the first cycle; then with the valves closed the mixed gases are compressed on the first up stroke, the second cycle; and at or near the top of the first up stroke, the compressed mixture of air and fuel ignites, by either a spark or by auto-ignition, and the mixture, or most of the gas mixture, combusts to produce a second downward stroke the third cycle, which is the power stroke; the second upward stroke, the fourth cycle, pushes the burnt gas mixture and the remaining un-burned gas mixture out of an open exhaust valve to complete the fourth cycle where the rotary or centrifugal motion created by the process is carried by the flywheel for the cycles to continue until either the fuel is shut off or the spark is discontinued.
The efficiency of the energy produced depends, among other variables, on the amount of air-fuel mixture drawn or forced into the cylinder and the compression volume ratio. The higher the compression volume ratio, the higher the efficiency. The compression volume ratio is limited, in the case of the gasoline engine, by the risk of premature ignition of the mixture and in the case of the diesel engine among other variables, by a sturdy and appropriate combustion chamber.
It is well known that four-cycle and other multi-cycle internal combustion engines produce exhaust gases that contain un-used energy in the form of un-burnt gasses. Many different approaches have been used to both try to capture the un-used energy within these unburned gases and to try to reduce atmospheric emissions caused by inefficient combustion.
Inventor is aware of U.S. Pat. No. 4,917,054 issued to Schmitz on Apr. 17, 1990, “Six-stroke internal combustion engine”. This is a reciprocating pistons engine, wherein six strokes used, they are the admission of air, the first compression accompanied or followed by a possible cooling, a second compression followed by a combustion, the first expansion producing a usable work, the second expansion producing usable work and finally the discharge of the combustion gases.